How to Check the Shaft Runout of Mechanical Seals?

There are three main reasons for the failure of mechanical seals parts

Seal face opening

When repairing different types of mechanical seals, 85% of seal failures are not caused by wear, but because they leaked before wearing. When the seal face opens, solid particles in the medium enter the seal face under the pressure of the liquid, and after the seal face closes, these solid particles embed themselves into the surface of the soft ring, which becomes a "grinding wheel" that damages the surface of the hard ring. Due to the fact that the moving ring or rubber ring is fastened to the shaft, when the shaft moves, the moving ring cannot adhere in time, which causes the seal face to open and the seal face to lag behind in closing, resulting in solid particles entering the seal face. At the same time, there are also solid particles between the shaft (shaft sleeve) and sliding parts, which affect the sliding of the rubber ring or moving ring. In addition, crystals will also be produced in the medium at the friction part between the rubber ring and the shaft (shaft sleeve), while solid materials will also be present at the spring, which will cause the seal face to open.

Overheating

Since heat is generated on the seal face, the temperature of the rubber ring used should be lower than the design specification. The use temperature of fluororubber and polytetrafluoroethylene is 216°C, and the use temperature of nitrile rubber is 162°C. Although they can withstand high temperatures, the rubber ring is at risk of continued vulcanization due to the high heat generated on the seal face, ultimately losing its elasticity and leaking. In addition, the heat between the seal faces will cause the medium to crystallize, such as carbon deposition, causing the sliding parts to be stuck and the seal faces to solidify. Moreover, some polymers will carbonize due to overheating, some fluids will lose lubrication, and even flash fire. Overheating can not only change the condition of the medium but also accelerate its corrosion rate, causing deformation of metal parts, cracking of alloy faces, and cracking of some coatings. Balanced mechanical seals should be chosen to reduce the specific pressure to prevent overheating.

Tolerance

The correct assembly tolerance is necessary for installing mechanical seals parts. The shaft (shaft sleeve) must have an appropriate surface roughness and correct size, but the manufacturers rarely provide tolerance data, which is critical for installation. The size accuracy and positional tolerance of mechanical seals must comply with the drawing requirements, and excessive tolerance will cause the seal to fail prematurely.

How to check the shaft deflection of mechanical seals parts?

Mechanical seals parts are a type of seal that is specially designed for reaction vessels, pumping equipment, and equipment that requires a high level of sealing. It is a part of some equipment that needs to be sealed and also a part that prevents external bacteria from entering. Mechanical seals parts enhance the sealing environment of the equipment. During routine inspections, in addition to checking its sealing performance, how should the shaft deflection be checked?

• The maximum shaft deflection should be less than 0.07mm. Check the jump on the sealing chamber surface. The jump on the sealing chamber surface should not exceed 0.13mm.

• If the sealing chamber surface is not perpendicular to the shaft, it may cause mechanical seal failure. Because the seal cover is fixed on the seal cover by bolts, excessive jump of the sealing chamber surface will cause the cover to be installed obliquely, resulting in the seal static ring tilting, causing the entire seal to shake abnormally.

• The wear of the auxiliary seal between different types of mechanical seals and the shaft or shaft sleeve will also be aggravated, and abnormal shaking of the seal will also cause wear and fatigue of the metal bellows or drive pins, causing premature failure of the seal.

Cooling is necessary to protect mechanical seals and prevent seal face burnout. In fact, water can be recycled and reused through a cooling tower with ordinary tap water, without the need for pure water. The main reason for cooling mechanical seals parts is that the speed is too high, causing the temperature to rise, which will cause damage to both the moving and static ring seals. If cooling water is not used, the cost of replacing the mechanical seal is not the only problem; it also wastes time to maintain it.